1. Technical Field
The present invention relates to a diagnosis device for a temperature sensor provided to an automobile transmission or the like, for example, and more particularly relates to suitably detecting an output voltage stuck (seized) malfunction of a temperature sensor.
2. Related Art
Automatic transmissions in automobiles, for example, have a temperature sensor to detect the temperature of automatic transmission fluid (ATF). ATF serves both as a hydraulic operating fluid and a lubricant. In a case where such a sensor malfunctions, control of the automatic transmission may encounter problems. Accordingly, various types of malfunction diagnosis techniques have been conventionally proposed.
For example, according to a technique described Japanese Unexamined Patent Application Publication (JP-A) No. 2004-11869 the detection value of the external air surrounding the automobile and the detection value of an fluid temperature sensor are compared. If the detection value of the fluid temperature is lower than the external air, the fluid temperature sensor is determined to be malfunctioning. Also, JP-A No. 2008-107089 describes a technique to diagnose a state in which temperature drifting of a thermocouple temperature sensor is occurring. Usage time at a temperature at which temperature drifting is apt to occur is weighted in accordance with the temperature, and the state of occurrence of temperature drifting is diagnosed based on an amount of drift estimated from an added value of weighted usage time.
An output voltage stuck malfunction may occur in an temperature sensor such as described above, where the output voltage sticks (seizes) at a certain output voltage. One technique for this is that an operating state where temperature change occurs is distinguished using accumulated running time, and malfunction is determined in a case where the output voltage of the temperature sensor is substantially unchanged over a predetermined amount of time. However, this technique may lead to erroneous diagnosis in cases such as where the amount of heat generated and the amount of cooling due to wind from driving are balanced, and the actual temperature of the object of measurement (e.g., ATF) is substantially constant.